The invention concerns a process and an apparatus for the production of plastic, in particular, thermoplastic laminates reinforced with a fiber web, wherein resin is applied to the fiber web in powder form, melted under the effect of pressure and temperature while pressed against the reinforcing webs to form a laminate.
Processes and apparatuses for the production of plastic laminates are known. Thus, for example, a process is known from German Pat. No. OS-23 12 816, in which two glass fiber mats are converged together at an angle and guided in a press gap between two rolls rotating in opposite directions. One of the rolls is a reversing or supporting roll for an endless belt which forces the circumference of the other roll to form therewith a press gap in which the glass fiber mats are acted upon by a predetermined pressure. Between the two glass fiber mats the resin is inserted in the form of an extruded strand which is to be pressed into the glass fiber mats during passage through the press gap. A similar effect is obtained when two endless belts are provided, which include mutually facing vertical flights between which are introduced the glass mats. A certain disadvantage of these known techniques involves the fact that undesirable air bubbles may be included with the resin and pressed into the laminate.
A process and an apparatus of the aforementioned type described in French Pat. No. 20 73 334 is further known, in which the resin is applied in powder form to the top side of a covering foil sheet which is transported on an endless belt. Thereafter, a reinforcing fiber web is placed on the powder layer, and the exposed side of the web is also provided with a layer of powder. The reinforcing fiber web is thus conducted while embedded on both sides in a layer of resin powder and is subsequently press-formed into a laminate in a press under the effect of heat, optionally with the addition of further reinforcing webs and layers of powder. A disadvantage consists of the fact that the resin powder penetrates differentially from the bottom and the top sides of the reinforcing fiber web, so that after pressing, a laminate with an asymmetrical structure is obtained. Another disadvantage involves the risk that air may be included in the pressing zone, because, as in other known processes, the resin is only capable of filling all of the cavities of the reinforcing fiber web when in the liquid state rather than in a powder state.
It is, therefore, an object of the invention to enable the reinforcing fiber mats to be impregnated while minimizing the inclusion of air and in such manner that a laminate with a symmetrical structure is obtained.